1. Field of the Invention.
The invention relates to a radar system adapted for shipboard operation in which a gyro compass produces signals which are used to operate a bearing scale centered around the display screen of the radar system and for providing stabilization of the radar display so that the radar presentation upon the display screen does not rotate along with rotation of the ship. The invention also includes a digital display of the ship's heading.
2. Description of the Prior Art.
Shipboard radar systems customarily include a gyro compass which produces incremental heading information to the radar system for rotation of a true bearing scale, providing north stabilization of the radar display, and for providing true motion correction. The most common gyro compass systems have either stepper motor or synchro-types of outputs. In the case of a stepper motor, three pole sets are commonly used with either 10' or 20.degree. bearing steps per output pulse. Pulse amplitudes of 35, 50, or 70 volts are normally employed. Synchro outputs, which are ordinarily three-phased, produce analog outputs representing either 1.degree. or 2.degree. of bearing per 360.degree. of shaft rotation. The rotor is driven from a supply frequency of either 50 or 60 Hz with commonly used voltages of 50, 60, 62, 115, 125, and 150 volts. The stator voltages are known to range between 20 and 90 volts with 20, 24, 57, 68, 82, and 90 volts being used in the most common commercially available units.
In the past practice, it has been customary for the gyro compass to drive the bearing scale and resolver for north stabilization separately through separate electronic circuits and mechanical linkages. It was also customary with past concepts to design new compass drive circuitry and mechanical components for each type of stepper motor or synchro output with the wide possibility of output voltages and operating conditions. This practice was, of course, expensive, time consuming, and made new installations expensive.
A further problem with prior compass drive systems was the arrangement provided for aligning the true bearing scale and/or the north stabilization resolver to the ship's heading. Since none of the gyro compasses commonly available provide a north stabilization or "homing" pulse, there was an ambiguity in the output of the gyro compass. Loss of synchronization due to rapid turning or loss of electrical power to the equipment had to be corrected by manual resetting. In past practice, a thumb wheel control was provided for correcting the resolver while a clutch and handle control was provided for correcting the position of the true bearing scale. Each of these controls had to be set separately.